Apparatus for portable fuel cells and operating method thereof

ABSTRACT

Disclosed are an apparatus for portable fuel cell and an operation method thereof, wherein stabilization state after initial operation can be determined using OCV.

TECHNICAL FIELD

The present invention relates to a whole fuel cell apparatus (referredhereinafter as “apparatus for portable fuel cell”) for power supply ofportable electronic appliances, including a secondary battery, a fuelcell, and a power regulator, and more particularly to an apparatus forportable fuel cell wherein smooth initial operating is possible, energylosses can be minimized, and as well stable and efficient energymanagement is possible, and an operating method thereof.

BACKGROUND ART

An apparatus for portable fuel cell is used as a power source havingoutput ranging from W level to kW level (e.g., 1 W˜5 kW) in variousappliances, such as mobile phones, notebook computers, (industrial ormilitary) humanoid robots, emergency power sources, electricwheelchairs, military communication devices, or the like. As a fuel celldirectly applicable to such apparatus for portable fuel cell, there is amodified hydrogen fuel cell (using methanol, diesel, natural gas, or thelike), a direct liquid fuel cell (using methanol, formic acid, ethanol,dimethylether, methylformate, borohydrides, or the like), a hydrogenfuel cell using a hydrogen storage tank, or others.

However, the conventional development has been mainly focused on anappliance itself to which the apparatus for portable fuel cell isapplicable as a power source, or an appearance after the apparatus forportable fuel cell has been installed. Like this, as a result of suchprior research for the peripheral things other than the apparatus forportable fuel cell itself, there has been, in fact, hardly studied aresearch for energy management required for commercialization of theapparatus for portable fuel cell.

In particular, there has been no ideas to minimize losses of energyproduced from the apparatus for portable fuel cell, to implement stableand efficient energy management, and to consider selection andarrangement of the components in the apparatus for portable fuel cell inview of such energy management.

DISCLOSURE Technical Problem

Accordingly, the present invention has been made to solve the abovementioned problems, and an object of the present invention is to providean apparatus for portable fuel cell and an operating method thereof,wherein losses of energy produced from the apparatus for portable fuelcell can be minimized, stable and efficient energy management can beimplemented, and selection and arrangement of the components in theapparatus for portable fuel cell can be carried out in view of suchenergy management.

Technical Solution

There is provided an apparatus for portable fuel cell comprising: a fuelcell comprising a unit cell or a stack of the unit cells; a secondarybattery which is chargeable and dischargeable; and a power managementsystem (PMS) having a DC-DC converter, the PMS receiving power producedfrom the fuel cell and supplying the power to an appliance, beingconnected with the secondary battery to receive or supply power,supplying power for operating the fuel cell, measuring voltage of thefuel cell and regulating power supply based on the measurement, whereinthe PMS is supplied with power from the fuel cell at a stabilizationstate that voltage measured from the fuel cell reaches a constant stateafter initial operation of the fuel cell.

In an embodiment of the invention, the PMS measures whether or not thevoltage of the fuel cell exceeds an open-circuit voltage (OCV) value ofthe unit cell or the stack thereof when the voltage of the fuel cell iselevated upon the initial operating, and after a time, whether or notthe voltage of the fuel cell reaches the OCV value again, and issupplied with the power from the fuel cell after the two timesmeasurement.

In an embodiment of the invention, when the voltage reaches within ±5%of OCV value after the time, the PMS determines that the voltage reachesthe OCV value, and is supplied with power from the fuel cell.

In an embodiment of the invention, the secondary battery supplies thepower of 10 to 15% of the total power produced from the fuel cell asinitial operating power of the fuel cell.

In an embodiment of the invention, the consumed power of the secondarybattery for the initial operating power of the fuel cell is suppliedfrom the PMS until the completion of its full charging, and then theconnection between the PMS and the secondary battery is cut off.

In an embodiment of the invention, when the fuel cell reaches itsperformance degradation stage after its normal operation state so thatthe potential thereof reaches below limit potential, the PMS stops powersupplying to the fuel cell so as to stop the operating of the fuel cell,and is supplied with power from the secondary battery.

In an embodiment of the invention, the PMS keeps the operation potentialof the fuel cell at 40 to 60% of use potential of the appliance so as tomaintain the efficiency of the DC-DC converter to be 85 to 90% or more.

In an embodiment of the invention, the number of separators and an areaof MEA of the fuel cell are controlled so that the operation potentialdoes not exceed 60%.

There is provided a method of operating an apparatus for portable fuelcell, wherein the apparatus for portable fuel cell comprises a fuel cellcomprising a unit cell or a stack of the unit cells; a secondary batterywhich is chargeable and dischargeable; and a power management system(PMS) having a DC-DC converter, the PMS receiving power produced fromthe fuel cell and supplying the power to an appliance, being connectedwith the secondary battery to receive or supply power, supplying powerfor operating the fuel cell, measuring voltage of the fuel cell andregulating power supply based on the measurement, the method comprisingthe steps of: supplying initial operation power from the secondarybattery to the fuel cell (S1); supplying power from the fuel cell to thePMS at a stabilization stage that voltage measured from the fuel cellreaches a constant state after initial operating of the fuel cell (S2);supplying power from the PMS, which is supplied with power, to anappliance, the fuel cell, and the secondary battery (S3); and stoppingpower supplying from the secondary battery to the fuel cell when thepower is supplied from the PMS to the fuel cell (S4).

In an embodiment of the invention, the PMS measures whether or not thevoltage of the fuel cell exceeds an open-circuit voltage (OCV) value ofthe unit cell or the stack thereof when the voltage of the fuel cell iselevated upon the initial operating, and after a time, whether or notthe voltage of the fuel cell reaches the OCV value again, and issupplied with the power from the fuel cell after the two timesmeasurement.

In an embodiment of the invention, in the step S2, when the voltagereaches within ±5% of OCV value after the time, the PMS determines thatthe voltage reaches the OCV value, and is supplied with power from thefuel cell.

In an embodiment of the invention, in the step S1, the secondary batterysupplies the power of 10 to 15% of the total power produced from thefuel cell as initial operating power of the fuel cell.

In an embodiment of the invention, in the step S3, the secondary batteryis charged with surplus power that is left after the power is suppliedto the appliance and the fuel cell.

In an embodiment of the invention, the PMS keeps the operation potentialof the fuel cell at 40 to 60% of use potential of the appliance so as tomaintain the efficiency of the DC-DC converter to be 85 to 90% or more.

In an embodiment of the invention, the number of separators and an areaof MEA of the fuel cell are controlled so that the operation potentialdoes not exceed 60%.

In an embodiment of the invention, the method further comprises the stepof: stopping power supplying from the PMS to the secondary battery, uponthe full charging of the secondary battery (S5).

In an embodiment of the invention, the method further comprises the stepof: stopping power supplying from the PMS to the fuel cell so as to stopthe operating of the fuel cell, and allowing the PMS to be supplied withpower from the secondary battery, when the fuel cell reaches itsperformance degradation stage after its normal operation state so thatthe potential thereof reaches below limit potential (S6).

Advantageous Effects

According to the present invention, by means of initial operatingdetection, efficient conversion of operating potential, minimum use offuel concentration in a fuel cell, maximum use of a secondary batteryupon the stoppage of the operation of the fuel cell, etc., it ispossible to minimize losses of energy produced and to carry out stableand efficient energy management. In addition, by means of selection andarrangement of the components in the apparatus for portable fuel cell inview of such energy management, it is possible to increase economy andavailability of the apparatus for portable fuel cell.

In particular, in the present invention, since determining the initialoperating based on the open-circuit voltage (OCV) has reliability of 95%or more, it is stably controlled to have optimum operating potential andminimum energy losses, thereby keeping the performance of the apparatusfor portable fuel cell constant.

Furthermore, the apparatus for portable fuel cell of the presentinvention can be used not only for the apparatus for portable fuel cellbut also for optimum power management in various kinds of fuel cellsystems.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of structure of an apparatus for portablefuel cell according to an embodiment of the present invention.

FIG. 2 is a view illustrating an operation of an apparatus for theportable fuel cell in their initial operation state and normal operationstate in an embodiment of the invention.

FIG. 3 is a graphical diagram illustrating variation of fuel cellpotential according to operating time in an initial operation state anda normal operation state in an embodiment of the invention.

FIG. 4 is a graphical diagram illustrating a detected response timeresult of an apparatus for portable fuel cell in an initial operatingstate and a normal operation state in an embodiment of the invention.

FIG. 5 is a schematic view illustrating the operation (performingminimum power management) of an apparatus for portable fuel cell in thestage of performance degradation of the fuel cell after a normaloperation state in an embodiment of the invention.

FIG. 6 is a graphical diagram illustrating variation of fuel cellpotential according to operating time in the stage of fuel cellperformance degradation after a normal operation state in an embodimentof the invention.

FIG. 7 is a graphical diagram illustrating a detected response timeresult of an apparatus for portable fuel cell in the stage ofperformance degradation of the fuel cell after a normal operation statein an embodiment of the invention.

FIG. 8 is a graphical diagram illustrating efficiency of a DC-DCconverter according to input potential in an apparatus for portable fuelcell according to an embodiment of the invention.

MODE FOR INVENTION

Hereinafter, an apparatus for portable fuel cell and an operating methodthereof according to the embodiments of the present invention will bedescribed in detail.

In the context, “fuel cell” can be referred to that it also comprises afuel supply unit, a fuel supply pump, a gas supply pump, a cooling fan,a BOP, etc., which are generally accompanied by fuel cell, as well asunit cell or stack of the unit cells.

FIG. 1 is a schematic view of structure of an apparatus for portablefuel cell according to an embodiment of the present invention.

As illustrated in FIG. 1, the apparatus for portable fuel cell accordingto an embodiment of the invention includes a fuel cell 10 consisting ofa unit cell or a stack of the unit cells, a chargeable, dischargeablesecondary battery 31, and a power management system (PMS) 30 formanaging power supply in the apparatus. The PMS receives power(voltage-current) produced from the fuel cell 10 and supplies it to anappliance 40 or the secondary battery 31, or receives power again fromthe secondary battery 31. The PMS includes a DC-DC converter (not shown)and a voltmeter (not shown) for measuring a voltage of the fuel cell 10in real time. Herein, the PMS 30 controls a voltage value correspondingto the specification of the appliance 40 connected to the apparatus forportable fuel cell, or corresponding to the parts (a liquid pump 12, agas pump 20, a cooling fan 21, a BOP 22, or the like) in the apparatusfor portable fuel cell. The DC-DC converter in the PMS 30 enhances theproduced energy suitably to a target voltage.

The fuel cell 10 is provided with general devices which can be providedto fuel cell. That is, the fuel cell 10 includes a fuel storage unit 11,a fuel supply pump 12 for supplying fuel from the fuel storage unit 11to the fuel cell 10 composed of a unit cell or a stack of the unitcells, an air pump 20 for supplying air to the fuel cell 10, a coolingfan 21 for cooling the fuel cell 10, a BOP 22 connected to the fuel cell10, and the like.

The air pump 20, the cooling fan 21, and the BOP 22 are operated usingpower supplied first from the secondary battery 31 so that the fuel cell10 is operated to produce electric power. As the secondary battery 31,secondary battery having super smaller capacity of e.g., 5V DC, 12V DC,or 21V DC can be used. Although the capacity can be changed according tothe production power of fuel cell, the capacity corresponding toapproximately 10-15% of the total power can be preferably used.

For example, optimum energy requirement of the parts (liquid pump 12,gas pump 20, etc.) for operating 30 Whr fuel cell 10 is approximately 6W, and in the case where stabilization time is set to below 10 minutes,the secondary battery 31 of approximately 1 Whr (which corresponds toapproximately 3% of output per hour/0.3% of the total output) isrequired. For reference, in case of a recently developed fuel cell fornotebooks, the output per hour is from 20 to 30 Whr, and the totaloutput is approximately 300 W.

As described later, consumed power of the secondary battery 31 ischarged with surplus power of the power to be used in the appliance 40,and when the secondary battery is fully charged, the power iscontinuously consumed only by the connection between the battery and theappliance so that the connection is cut off to prevent the energyefficiency from reducing.

Power switches are provided between the fuel cell 10 and the secondarybattery 31 and the PMS 30, or between the secondary battery 31 and theair pump 20, the cooling fan 21, and the BOP 22, or between the air pump20, the cooling fan 21, and the BOP 22 and the PMS 30 to turn on/off thecurrent flow, and the switches are controlled to turn on/off by the PMS30.

Meanwhile, a capacitor 33 can be additionally provided to the PMS 30 inorder to consider the energy supply to the appliance 40 according todynamic energy consumption of the appliance 40.

FIG. 2 is a view illustrating an operation of an apparatus for theportable fuel cell in their initial operation state and normal operationstate in an embodiment of the invention.

In FIG. 2, as described above, initial power is supplied from thesecondary battery 31 to the parts 12, 20, 21, and 22 to operate the fuelcell 10. Herein, “on 1” of switch denotes the power supply. Such initialpower supply is stopped in case of “on 3” condition (i.e., “on 1” isswitched into “off 1”).

Upon the production of power by operating the fuel cell 10, the producedpower is supplied to the PMS 30. Herein, initially produced power is notsupplied directly, but the power is supplied from the fuel cell 10 tothe PMS 30 in case of a stabilization state (described further in detailbelow) in which voltage measured from the fuel cell 10 becomes constantafter the initial operating. Herein, “on 2” denotes the power supply.

Meanwhile, the PMS 30 supplies power received from the fuel cell 10 tothe appliance 40, the secondary battery 31, and the parts 12, 20, 21,and 22. Herein, the power supply is denoted as “turn on 3” and “turn on4” of the switch. Upon the completion of charging in the secondarybattery 31, the power supplied to the secondary battery 31 is cut off(i.e., “turn on 4” is switched into “turn off 2”). After the fullcharging of the secondary battery 31, when the PMS 30 is connected tothe secondary battery 31 (i.e., not being into “turn off 2”), the energyefficiency of the whole apparatus for portable fuel cell can be reduceddue to a phenomenon that a certain amount of energy is consumed.

An important fact in the above operating is how the initialstabilization state is determined.

FIG. 3 is a graphical diagram illustrating variation of fuel cellpotential according to operating time in an initial operation state anda normal operation state in an embodiment of the invention.

As illustrated in FIG. 3, while fuel and air are supplied, the outputpotential of the fuel cell is elevated from 0V to a maximum point (e.g.,11V or less in case of a direct liquid fuel cell system using 15 sheetsof bipolar plate separators), and then the output potential is graduallystabilized.

However, generally, the unit cell or the stack thereof in the fuel cell10 is stabilized after a constant time, and the stabilization time canbe varied according to specification and output range of the unit cellor the stack thereof.

Thus, it is not suitable that the stabilization of the operation of thefuel cell 10 is determined based on time concept, and even in case ofthe consideration of the experimental value, the unstable state of thefuel cell 10 may be caused, and the dynamical operation of the appliance40 may be problematic.

Thus, it is preferable that the stabilization state is determined bychecking OCV that the unit cell or the stack thereof can show.

In specific, OCV, which the unit cell or the stack thereof can indicate,is measured in advance and is input to the PMS 30. The PMS 30 detectsvoltage of the fuel cell 10 in real time. Further, when voltage iselevated from 0V upon the initial operating, PMS 30 checks whether thevoltage exceeds the OCV value, and after a certain time, PMS 30 checksagain whether the voltage reaches the OCV value. To this end, when theOCV value is checked two times, the PMS 30 is set to be supplied withpower from the fuel cell 10.

Meanwhile, since the invention uses the OCV value which is thestabilization state value, upon the secondary voltage measurement fordetecting whether the voltage reaches the OCV value, the PMS does notuse an absolute value for voltage, but the PMS determines that thevoltage reaches the OCV value if the voltage is detected to be within±5% of the OCV value, thereby operating the fuel cell 10.

In case of the direct liquid fuel cell coupled with 15 sheets of bipolarplate separators, the OCV of each separator is 0.5˜0.75V. Thus the totalpotential of 7.5˜11.25V corresponding to 15 sheets of the separatorsbecomes detected two times.

Herein, as described above, the power output from the fuel cell 10 issupplied to the parts, such as the BOP 22, via the PMS 30, and at thesame time, charges the discharged secondary battery 31. After completionof full charging of the secondary battery 31, the power source connectedis cut off.

FIG. 4 is a graphical diagram illustrating a detected response timeresult of an apparatus for portable fuel cell (voltage change of directliquid fuel cell using 15 sheets of the separators) in an initialoperating state and a normal operation state in an embodiment of theinvention.

As seen from FIG. 4, the voltage is elevated from 0V to approximately11.7V while fuel and air are supplied, and reaches a stabilization stagewithin about 5 minutes.

The OCV of the direct liquid fuel cell using 15 sheets of separators isapproximately 8.0V, and as shown in FIG. 4, when the OCV of the realstack of the fuel cell 10 reaches 8V, current is output to begin anoperation.

Like this, the present invention carries out operation consideringwhether an initial stabilization is obtained. To determine the initialstabilization based on absolute time may cause a problem in thatstability of the apparatus and efficient use of fuel as well asminimization of energy losses of the whole apparatus are not satisfiedbecause respective states and conditions of the unit cells or the stackare not considered. Therefore, it is preferable that whether an initialstabilization is obtained be determined using OCV.

FIG. 5 is a schematic view illustrating the operation (performingminimum power management) of an apparatus for portable fuel cell in thestage of performance degradation of the fuel cell after a normaloperation state in an embodiment of the invention. FIG. 6 is a graphicaldiagram illustrating variation of fuel cell potential according tooperating time in the stage of fuel cell performance degradation after anormal operation state in an embodiment of the invention.

Referring first to FIG. 6, FIG. 6 illustrates that the operatingpotential of the fuel cell is degraded in its performance after a normaloperation state, thereby reaching output limit potential Vmin of thefuel cell.

This means that while fuel supplied from the fuel supply 11 via aconcentration adjuster is continuously consumed, 90˜95% or more ofinitial chemical energy (i.e., energy density) of fuel cell is consumed(mass transfer limit phenomenon) so that the performance of the fuelcell 10 is degraded. In addition, such abrupt reduction in operationpotential may be caused from deterioration of a catalyst, a polymericmembrane, a separator and an electrode due to long-term use anddynamical operating.

Referring to FIG. 5, when the output potential of the fuel cell 10reaches limit potential, the power output of the fuel cell 10 is cutoff. Herein, the switch is denoted as “on 4”. Further, in this case, itneeds not the operating of the fuel cell 10, so that the PMS 30 controlsthe operation of BOP 22 to be stopped, which is operating the fuel cell10. Herein, the switch is denoted as “off 3”. The operation at the limitpotential or less means the operation in case of the supply of lowconcentration fuel or the operation of the stack at high currentdensity, so that there may be caused a problem in stability andendurance of the fuel cell 10.

In addition, the stoppage in the operation of the BOP 22 for managingthe operating of the fuel cell 10 at limit potential is to maximizeenergy utilization of the secondary battery 31. That is, even whenfurther power output from the fuel cell 10 does not occur any more, ifthe BOP 22 is operated, the lifetime of the secondary battery 31 usedfor initial operating and fuel substitution can be reduced.

Meanwhile, the operation is stopped for fuel re-supply and checking ofthe fuel cell 10. Herein, the secondary battery 31 is in charge of thepower for operating the appliance 40 (denoted as “on 5”). In case wherefuel is simply re-supplied, the time for re-supply is 5 minutes or less,which does not cause any problem in re-operating the whole apparatus.

FIG. 7 is a graphical diagram illustrating a detected response timeresult of an apparatus for portable fuel cell in the stage ofperformance degradation of the fuel cell after a normal operation statein an embodiment of the invention.

As shown in FIG. 7, while the operation time becomes longer, theconcentration of the fuel cell is reduced and the operating potential of5.3V reaches limit potential of 4.0V. Then, the potential reachesmaximum potential and then the stabilization stage of 8.0V.

FIG. 8 is a graphical diagram illustrating efficiency of a DC-DCconverter according to input potential in an apparatus for portable fuelcell according to an embodiment of the invention.

To make the efficiency of the DC-DC converter above 85%˜90%, i.e., tominimize the energy losses, the fuel cell should secure operationpotential of 40˜60% of the use potential of the appliance. For example,most of portable fuel cell devices is operated while the appliance is in12V DC. Herein, the operation potential of the direct liquid fuel cellusing 15 sheets of separators is made to be approximately from 4.8 to7.2V. The efficiency of elevating voltage from a level of operatingpotential below 40%, e.g., 4V to 12V is 80% or less. Meanwhile, in caseof using the fuel cell 10 having operating potential of 5.5V, the energyloss is 10%, which is on the very small level. Further, when thepotential of 60% or more, e.g., 7.5V or more is secured, the efficiencyis increased, but the number of separators to be stacked and the area ofMEA should be increased, which is not preferable.

Therefore, the number of the separators and/or the area of MEA should bedetermined in consideration of the amount of such energy loss. Forexample, in the case of a hydrogen fuel cell using, e.g., modifiedhydrogen, when about 10 sheets of the separators are used, the operatingpotential can be maintained to be 6V or more.

INDUSTRIAL APPLICABILITY

The present invention relates to a whole fuel cell apparatus for powersupply of portable electronic appliances, which includes a secondarybattery, a fuel cell and a power regulator.

The invention claimed is:
 1. An apparatus for portable fuel cellcomprising: a fuel cell comprising a unit cell or a stack of the unitcell; a secondary battery which is chargeable and dischargeable, andconnected to the fuel cell to supply an initial power to the fuel cell;and a power management system (PMS) having a DC-DC converter and beingconnected with the secondary battery to receive or supply power, andbeing connected with the fuel cell to receive power or supply power, andbeing connected with an appliance to supply power, wherein the PMS isprogrammed to measure voltage of the fuel cell and regulate power supplybased on the measurement, wherein the PMS is programmed to be suppliedwith power from the fuel cell at a stabilization state that voltagemeasured from the fuel cell reaches a constant state after initialoperation of the fuel cell using the initial power from the secondarybattery, wherein the PMS is programmed to measure whether or not thevoltage of the fuel cell exceeds an open-circuit voltage (OCV) value ofthe unit cell or the stack thereof when the voltage of the fuel cell iselevated upon the initial operating is measured by the PMS, and after atime, whether or not the voltage of the fuel cell reaches the OCV valueagain, and to be supplied with power from the fuel cell after the twotimes measurement, and when the voltage reaches within ±5% of OCV valueafter the time, it is determined that the voltage reaches the OCV value.2. The apparatus for portable fuel cell of claim 1, wherein when thevoltage reaches within ±5% of OCV value after the time, the PMSdetermines that the voltage reaches the OCV value, and is supplied withpower from the fuel cell.
 3. The apparatus for portable fuel cell of anyone of claims 1 and 2, wherein the secondary battery supplies the powerof 10 to 15% of the total power produced from the fuel cell as initialoperating power of the fuel cell.
 4. The apparatus for portable fuelcell of any one of claims 1 and 2, wherein the consumed power of thesecondary battery for the initial operating power of the fuel cell issupplied from the PMS until the completion of its full charging, andthen the connection between the PMS and the secondary battery is cutoff.
 5. The apparatus for portable fuel cell of any one of claims 1 and2, wherein when the fuel cell reaches its performance degradation stageafter its normal operation state so that the potential thereof reachesbelow limit potential, the PMS stops power supplying to the fuel cell soas to stop the operating of the fuel cell, and is supplied with powerfrom the secondary battery.
 6. The apparatus for portable fuel cell ofany one of claims 1 and 2, wherein the PMS keeps the operation potentialof the fuel cell at 40 to 60% of use potential of the appliance so as tomaintain the efficiency of the DC-DC converter to be 85 to 90% or more.7. The apparatus for portable fuel cell of claim 6, wherein the numberof separators and an area of MEA of the fuel cell are controlled so thatthe operation potential does not exceed 60%.